Many forms of devices exist which are used to sense the relative position of a mechanical object relative to a reference position. For example, optical encoders are used commonly to sense rotational movement of one member relative to another member. In robotics, one member is in the form of an arm which is moved about a joint. Also, such encoders are used to keep track of rotational movement of a motor shaft relative to a frame on which it is mounted. Yet another application is in the turning of knobs of a control panel for adjusting an associated instrument. Traditionally, such knobs had a multiplicity of electrical contacts which a wiper moved across, with each contact corresponding to a predetermined knob setting.
Such apparatus tends to be relatively expensive. Optical transmitters and receivers are in themselves quite complex. A multiplicity of electrical conductors and contacts must be provided to accommodate each of the positions of a knob or other rotating member. They also require external power supplies to make them work. Elaborate or duplicate elements are also required in order to sense the direction of rotation of the member being moved. Physical contacts are subject to corrosion and dirt, and require careful and elaborate engineering to survive adverse environments. Further, optical encoders or potentiometers do not have any inherent detent action which would provide tactile feedback of knob position. If such is desired, it must be added to the assembly.
Many electrical systems are currently structured to use CMOS logic in order to take advantage of the low power and minimal drive requirements inherent in CMOS devices. In order to accommodate conventional devices, interface circuitry must be provided in order to produce voltage swings compatible with CMOS logic. Many conventional devices, such as potentiometers, are damaged if washed. This is particularly important during manufacture, where an assembly needs to be washed after soldering.